P0299
Turbocharger/Supercharger "A" Underboost Condition
Boost pressure under load is below the commanded value. Very common on turbodiesel and direct-injection turbo gasoline engines as the turbo system ages — typically a leaking boost pipe, a sticky variable-geometry vane assembly, or a wastegate that no longer holds.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
What we see in the workshop
ON FORD ECOBOOST
Underboost is one of the most common EcoBoost complaints we see. Before condemning the turbo, we pressure-test the charge air system — split or popped-off charge pipes, a leaking intercooler and a tired diverter valve account for most cases. It usually presents as limp mode under hard acceleration while the car drives normally when cold.
Symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
Common causes
Ordered by how often each turns out to be the cause.
- Leak in intercooler pipe or hoseCommon
- VGT vanes stuck (diesel, soot buildup)Common
- Wastegate stuck open or weak springPossible
- Turbo bearing worn (preceded by oil consumption / smoke)Less likely
Parts involved
- Turbocharger
- Intercooler
- Intercooler Pipe
- Wastegate Actuator
- VGT Actuator
P0299 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.